1) Book 2 ships only-- no High Guard!
2) A different map based on the Capitol premise from the Library Data of Adventure 2. (The Bottleneck Empire?) The Spinward Marches are still there, but most Empires are no bigger than a sector or two in size.
3) Piracy is not a flamewar here because pirates are built into the basic premise of the setting.
4) PC's actions can make a difference without them becoming Admirals or CEO's.
5) The Imperium board game is not necessarily grafted into future history of this setting.

Am I missing anything?

Library data from Adventures 1-3 sounds like the key thing to look at for background. Is there any other resources good to use?